This invention pertains to an apparatus for conveniently carrying out a fluorescent inspection on the interior surfaces of a hollow article such as a gas turbine engine shaft or rotor assembly.
Fluorescent penetrant inspection is a known technique for detecting surface cracks in metal articles. The fundamentals of fluorescent penetrant inspection are well known. A fluorescent penetrant is applied to the surface of interest. Excess penetrant coats the surface and seeps into any surface discontinuities such as scratches or cracks. Excess penetrant is then washed off the surface, leaving behind only residual penetrant trapped in the discontinuities. Upon exposure to ultraviolet (UV) light, the residual, entrapped penetrant fluoresces to reveal the presence of surface anomalies not discernible to the unaided eye. Subsequent examination of the surface under light in the visible portion of the spectrum is often necessary to determine if an anomaly is a potentially troublesome imperfection or merely an inconsequential scratch or other benign surface irregularity.
Fluorescent penetrant inspection is more complicated if the surface of interest is in the interior of a hollow article. Examples of such surfaces include the interior surfaces of gas turbine engine shafts, turbine rotors and compressor rotors. Specialized devices are required to view the surface and sometimes to apply the penetrant and wash away the excess.
One such specialized device is the apparatus described in U.S. Pat. No. 5,115,136. The apparatus includes appropriate light sources as well as canisters of penetrant, compressed air, water and a developer, all of which may be delivered to a desired inspection site by way of a fiberscope probe. The fiberscope also includes an eyepiece through which an inspector may view the site. Another specialized device is the borescope of U.S. Pat. No. 5,202,758. The described borescope includes means for determining the true physical size of a fluorescing anomaly. Despite the presumed merits of these devices, they are obviously hand-held, which makes it difficult for an inspector to obtain a steady, repeatable image or to view the image while engaging in related activities such as taking notes to record relevant observations or consulting manuals and instruction sheets. In addition, fiberscopes and borescopes of the type shown in the ""136 and ""758 patents have a narrow field of view, typically not much more than about four square centimeters, making it inordinately tedious to completely inspect a large surface.
U.S. Pat. No. 4,675,728 shows a device for inspecting the interior of pipes in a nuclear powerplant. The device is a carriage on wheels with a camera, appropriate light sources and a set of nozzles for directing fluorescent penetrant, water and air against an inspection site. The device is compact, having a height no more than about one third of the pipe diameter. In use, the device is inserted into the open end of a horizontal or inclined pipe with the carriage wheels contacting the pipe inner surface. The carriage is rolled along the pipe""s relatively uninterrupted interior surface to the desired inspection site by way of an xe2x80x9cumbilical cordxe2x80x9d comprising the various cables and supply lines necessary to service the camera, lights and nozzles. Alternately, the device may be lowered, again by way of the umbilical, to a desired location within a vertical length of pipe.
Despite the presumed merits of the pipe inspection carriage, it is not without shortcomings. With the carriage positioned as shown in FIG. 2 of the ""728 patent, only two 120xc2x0 segments of the pipe are inspectable, and then only with a certain amount of disassembly and reassembly of the device""s constituent parts. In addition, the device is ill suited for use in the interior of a turbine engine rotor assembly where the bores of axially successive rotor disks are separated by deep recesses. The axially alternating bores and recesses, unlike the axially uninterrupted inner surface of a pipe, would interfere with or prohibit rolling movement and precise positioning of the carriage. Even if a turbine engine rotor were oriented vertically (i.e. with its rotational axis vertical) and the pipe inspection apparatus lowered vertically into the rotor bore, it would be difficult to obtain a stable image of the inspection site because the inspection device would not be positively supported in the radial (horizontal) direction. Finally, the pipe inspection device is clearly adapted to treat and inspect only radially facing interior surfaces. No provisions are made to inspect surfaces at other orientations, for example the axially facing surfaces of a compressor or turbine disk.
Other types of illuminating and viewing devices may be of limited value because they include only a single, broad spectrum lamp with a single intensity adjustment. Such a lamp emits broad spectrum light comprising both ultraviolet and visible wavelengths. A filter capable of passing only the UV wavelengths is provided so that the device is operable in either a xe2x80x9cpure UVxe2x80x9d mode or in a xe2x80x9cbroad spectrumxe2x80x9d mode depending on whether or not the filter is engaged. An inspection technician scans the surface of interest in the UV mode (i.e. with the filter engaged to pass only ultraviolet wavelengths). The technician typically conducts the UV inspection with the lamp intensity adjustment set at or near its maximum because the UV light emitted by commercially available lamps is relatively weak. If the technician observes a fluorescing anomaly, he switches to the broad spectrum mode because the non-fluorescing surroundings of the anomaly are not readily visible under the pure UV light. The technician needs to illuminate the immediate environs of the anomaly with visible light so that he can view the anomaly in the context of its surroundings and better judge its significance. Unfortunately, the visible light emitted by commercially available lamps is substantially stronger and brighter than the UV light. Therefore, if the technician engages the broad spectrum mode without first lowering the intensity adjustment of the lamp, the excessively brilliant visible light not only overpowers the fluorescence emitted by the anomaly, but also completely obstructs the technician""s view of surface details that the visible light was intended to reveal. As a result, the anomaly is rendered temporarily indiscernible. Consequently, the technician is obliged to lower the intensity adjustment either before or after switching to the broad spectrum mode. However, lowering the intensity adjustment lowers the intensity of both the UV and the visible light, so that the visible light continues to overpower the fluorescence emitted by the anomaly. The absence of discernible fluorescence may cause the technician to lose track of the anomaly, forcing him to return to pure UV mode of illumination, raise the intensity adjustment to a higher level compatible with the weaker intensity pure UV light, and reacquire the anomaly. This obviously makes the technician""s task tedious and frustrating, especially when the surface being inspected is large.
It is, therefore, a principal object of the invention to provide an inspection apparatus that facilitates convenient and thorough fluorescent penetrant inspection of the interior surfaces of hollow articles such as gas turbine engine shafts and rotor assemblies.
It is a corollary object of the invention to provide a stable, repeatable image of a target region within the article and to achieve a generous field of view.
It is another corollary object of the invention to enable convenient inspection of axially facing surfaces within the article.
It is another corollary object of the invention to inspect radially facing interior surfaces of the article over a full 360xc2x0 of arc without the burden of reconfiguring the inspection apparatus.
It is another corollary object of the invention to inspect the interior of the article despite the presence of significant topographical irregularities such as the deep recesses between axially successive disks of a gas turbine rotor.
It is another corollary object of the invention to provide an apparatus and method by which selected target regions may be inspected without making repeated adjustments to the intensity of light illuminating the target and without significant risk of losing track of a fluorescing anomaly.
According to the invention, an apparatus for inspecting the interior surfaces of a hollow article includes a primary camera mounted at one end of a support arm for capturing a steady image of a target region to be inspected. The arm is translatable in a principal direction so that it may inserted into the interior of the article. The apparatus also includes ultraviolet and visible light sources for illuminating the target region and a video monitor for displaying the image.
According to one aspect of the invention, the light sources are independent sources with independent intensity adjustments so that the intensity of light emitted by either source can be adjusted without affecting the intensity of light emitted by the other source and so that an anomaly can be viewed simultaneously with both visible and UV light.
According to another aspect of the invention, the support arm is also translatable in a secondary direction perpendicular to the principal direction.
According to still another aspect of the invention, the apparatus includes an auxiliary viewing attachment, easily securable to the support arm. The auxiliary attachment has an auxiliary camera for viewing target regions angularly offset from the line of sight of the primary camera.
The invention is advantageous because it provides a stable, steady image of a target region inside a hollow article such as a turbine engine shaft or rotor assembly. The inventive apparatus also provides a generous, yet high resolution field of view since the cameras are mounted at an end of the arm proximate to the target region. The invention also offers 360xc2x0 of viewing coverage since the article, if properly supported, may be rotated about the camera to bring different regions of the article""s interior surface into the camera""s field of view.
Another advantage is the ease with which the inventive apparatus can be adapted, by means of the viewing attachment, to view target regions angularly offset from the line of sight of the primary camera. In particular, the attachment is positionable in the deep annular recesses between neighboring rotor disks in a gas turbine compressor or turbine rotor to capture an image of the axially facing disk surfaces.
Another advantage is the ability of the apparatus to traverse the entire axial length of a rotor despite the presence significant topographical irregularities.
Another advantage of the invention is its ability to provide simultaneous illumination with both visible and ultraviolet wavelengths while minimizing the need for repeated light intensity adjustments.